Assessment interviewing often takes place during the early stages of helping, which includes obtaining information about the client related to the client’s problem or area of change desired. During this stage of helping, the counselor is involved in “conceptualization or formulation” of the problem within counseling sessions or specifically within the assessment interview. Interviewing to assess entails a focus on all aspects of clinical concern, including physiology, cognition, behavior, duration, severity, relationships, and context. A detailed and thorough assessment interview that clarifies the problem holistically leads not only to accurate assessment but also, in later stages of helping, to amelioration. Assessment interviewing is viewed as the foundation of the therapeutic, counseling, and/or rehabilitation process. This chapter is on the assessment interview. It covers types and formats of assessment interviews. This overview is intended to orient the reader to the importance of depth, detail, and thoroughness within the assessment interview.